The term Chromagram used hereafter is meant to include optical structures that have a patterned or windowed substrate together with special effect coatings or layers supported by or supporting the patterned or windowed substrate. Chromagrams of various designs are described in US Patent Application Publication No. 2006/0285184, and used as security devices or for enhancing the security of products and for their aesthetic appeal.
One type of Chromagram is an optical structure that exhibits the effects of surface relief patterns, such as holograms or diffractive gratings, together with a pattern such as alphanumeric characters, bar codes, or graphical or pictorial designs, and additional optical effects in the regions around such pattern. Such structures are described in US Patent Application Publication No. 2006/0077496 in the name of Argoitia et al. published Apr. 13, 2006, referred to hereafter as '496. Another Chromagram-type structure is described in US Patent Application Publication No. 2005/0128543 in the name of Phillips et al. In '496 patterned substrates having windowed regions that one can see through, are coated with optically variable (OV) coatings or optically variable inks that can be seen through the windows. For all intents and purposes, all references described heretofore or hereafter are incorporated herein by reference.
By use of the term “patterned” layer, it is meant that a reflective, opaque, or partially transmissive layer is applied over a substrate which may be planar or have a surface relief pattern therein, in a manner that forms a desired “pattern” or design. By way of non-limiting examples, the patterned reflective layer can be formed in the shape of letters, numerals, bar codes and/or graphical or pictorial designs.
One type of the surface relief pattern is a demetalized (demet) hologram described in U.S. Pat. Nos. 5,314,767, 6,616,190, and 7,081,819. To enhance the security of holograms and to prevent contact copies being made, a technique was developed for making holograms by a process of demetallization. Demetalized holograms and patches are used in passports and ID cards to protect photographs and data.
Although not limited thereto, this invention primarily relates to types of Chromagrams, made with optical and, or, magnetic effect hot stamp adhesive having flakes and/or colorant therein. Heretofore, a desirous quality of adhesives used to bond two substrates together, wherein one substrate is to be seen through the other, has been for the adhesive to be substantially transparent and having required bonding properties. Therefore the goal has been to have an adhesive that “appears” to be as invisible as possible, and substantially matched in refractive index to the substrates with which it is bonding, thereby substantially un-affecting light passing therethrough.
Hot stamp transfer foils have been provided in conjunction with hot stamp machines to affix images onto various substrates such as paper, plastic film and even rigid substrates. Hot stamping is a dry process. One commercially available machine for hot stamping images onto substrates is the Malahide E4-PK produced by Malahide Design and Manufacturing Inc. Machines of this type are shown and described on the Internet at www.hotstamping.com. Simplistically, in a hot-stamping process, a die is attached to the heated plate which is pressed against a load roll of hot stamping foil to affix the foil to an article or substrate. A roll on transfer process could also be used in this invention. In this case, the article substrate and the adhesive (UV or heat activated) is brought together at a nip to effect the transfer of the hot stamp layer to the article substrate.
An image is typically formed by utilizing a metal or silicone rubber die into which the desired image has been cut. This die is placed in the hot stamping machine and is used to press the image into hot stamp foil utilizing a combination of heat and pressure. The back side of the foil is generally coated with a dry heat activated, thermo set adhesive, for example an acrylate based adhesive. Upon the application of heat, the adhesive becomes tacky in regions of the heated image and adheres to the paper or plastic substrate.
Hot stamping is described or mentioned in the U.S. Pat. Nos. 5,002,312, 5,059,245, 5,135,812, 5,171,363, 5,186,787, 5,279,657 and 7,005,178, in the name of Roger Phillips of Flex Products Inc. of Santa Rosa Ca. Additional details of a hot stamping process may be found on pages 440-445 of the Modern Plastics Encyclopedia, 1979-1980.
Aforementioned U.S. Pat. No. 5,059,245 describes forming an optical coating upon a substrate wherein the optical coating in one embodiment comprises optically variable flakes applied within a carrier as paint or ink which is then dried or cured upon the substrate.
Optical effect flakes in an adhesive may have one or more predetermined optical characteristics; for example, flakes may be optically variable changing color with a change in angle of incident light, or flakes may be diffractive, or may have covert symbols therein or thereon, or the flakes may simply be reflective or absorptive. In some instances, optical effect flakes have a combination of optical effects, for example they may be diffractive and color shifting, or they may be diffractive and reflective, or diffractive and highly absorptive depending upon the desired effect. Furthermore flakes having different optical effects may be mixed together in desired ratios. Pigments that may be added include those based on interference, for example mica based pigments, Fabry Perot type pigments, liquid crystal type pigments, including those that color shift with viewing angle, non-shifting pigments like gold and nickel, and other metallic flakes. Dyes and or other pigments may be added to the adhesive to modify the colors of the interference and/or diffractive pigments, including covert platelets, known as charms or taggants, and other shaped particles. The examples of covert flakes include, but not limited to, charms or taggants as taught in US Patent Application Publication No. 2006/0035080 incorporated herein by reference, shaped pigments as disclosed in US Patent Application Publication No. 2006/0035080, magnetic flakes, fluorescent pigments, standard UV activated to form visible light, or specialized anti-Stokes materials UV activated to form visible light.
Heretofore, in instances when a layer of material such as an ink coated substrate having optically variable flakes therein was hot stamped to another substrate or object, prior to hot stamping, a heat-activated adhesive layer, typically 2-20 microns thick, was applied to the substrate or object to adhere the layer of material to the substrate or object by applying suitable heat and pressure.
In relation to FIGS. 1a and 1b, U.S. Pat. No. 7,029,745 teaches a method of affixing a security article, such as security article 30, to a carrier substrate 66 through a hot-stamping process. FIG. 1a shows security article 30 with a release layer 62 formed on one side of a light transmissive substrate 24, such as an acrylic coating with an interference pattern formed thereon. The release layer 62 allows security article 30, including substrate 24, absorber layer 18, dielectric layer 20 with optical interference pattern 15, and reflector layer 22, to be released from carrier structure 64 during the hot-stamping process.
As shown in FIG. 1b, a release layer 62 and carrier structure 64 are removed when security article 30 has been applied to an object such as a carrier substrate 66 by hot-stamping, with security article 30 being coupled to carrier substrate 66 by way of adhesive layer 68. Sometimes the release stays with the substrate 62. The bonding of adhesive layer 68 against carrier substrate 66 occurs as a heated metal stamp (not shown) comes into contact with carrier structure 64. The heated metal stamp simultaneously forces adhesive layer 68 against carrier substrate 66 while heating adhesive layer 68 to more effectively bond to carrier substrate 66. Furthermore, the heated metal stamp softens release layer 62 thereby aiding in releasing security article 30 from carrier structure 64 which is subsequently discarded. Once security article 30 has been attached to carrier substrate 66, the image produced by security article 30 is viewed from substrate 24 toward optical coating 16.
In the field of hot-stamping, a plurality of commercially available adhesives have been developed to provide required adhesion of foils to same and other materials, under heat and pressure. Although these heat-activated adhesives have performed their intended function, they have not provided additional functions now perceived to be highly useful.
For example, the inventors of this invention have discovered that these dry heat activated adhesives can be applied to a substrate and can be preloaded or premixed into the adhesive with special optical effect flakes, such as magnetic flakes, magnetically alignable flakes, magnetic flakes with color shifting properties, color shifting flakes, color switching flakes, diffractive flakes and or covert flakes bearing indicia also known as charms.
It is an object of this invention to provide a hot stamp adhesive, that has therein, special effect flakes, and wherein the flakes can be seen through one or more layers the adhesive is bonding. It was not anticipated that acceptable adhesion would result when optically variable pigment was added to the hot stamp adhesive. The adhesive could also be printed in a pattern so as to affect a patterned transfer even though a flat die would be used to make the hot stamp transfer. Printing the adhesive rather than having an image in the die of the hot stamper results in a better transferred image with higher definition without “fringe” often seen in foil type transfers. Fringe refers to the ragged edges of the foil image when hot stamped onto surface of paper, for example. The problem is evident often in the hot stamp transfer of the letter “A” where the triangle of the letter “A” is covered with foil.
It is an object of the invention, to provide a Chromagram where the provision of a discrete special effect layer is obviated, by adding special effect flakes to a hot-stamp adhesive for to bond two objects together. This makes for a product that easier to manufacture and reduces manufacturing costs.
It is an object of this invention to hot stamp a substrate to another substrate or object, wherein optical effect adhesive bearing optical effect flakes is solely used as an adhesive.
Security threads have been known for some time. U.S. Pat. No. 4,186,943 to Lee describes a windowed security thread that is contained within the banknote paper. Lee uses diachronic coatings, in all-dielectric optical stack, having a symmetrical design so that the same reflected and transmitted color and color shift is seen from either side of the paper through elongate windows of the paper substrate. In one embodiment, paper is removed at various points over the embedded security thread to allow the thread to be more clearly seen. Furthermore, unfortunately, counterfeiters have at their disposal from the packaging field commercially available transparent film made from hundreds of alternating layers of polymeric films that display similar color shifting and reflection and transmission characteristics as found in '943. See http://www.ptonline.com/articles/200603fa1.html. This makes foils based on all-dielectric suspect as an anti-counterfeit system. US Patent Application Publication No. 2006/0255586 by Lazzerini describes a security device composed of holographic regions with a continuous metal layer of aluminum but with variations in its thickness. In co-pending application, WO2004014665 by Lazzerini, the method of “thinning” the deposited aluminum is by chemical etching after some areas of the aluminum are protected by a transparent ink adapted to preserve the aluminum by the attacks of acid substances. The aluminum is thinned from an optical density of 1.8, transmission of 1.6%, down to 0.7 optical density or about 20% transmission, in the “A” portion, item 3 of the '586 patent application. In other words, the aluminum is opaque in areas other than the “A” portion and only semi-transparent in the “A” areas. The use of magnetic elements in register with the holographic elements is mentioned but does not indicate the nature of the magnetic elements. Another version of the invention uses color shifting ink between the backing layer of Polyethylene Terephtalate (PET) and the continuous aluminum metal layer. The type of color shifting ink is not defined—they could be mica based transparent color shift with angle pigments, or liquid crystal color shift inks both of which are transparent—in our invention the pigment is opaque). At any rate, Lazzerini does not teach a color shift material based on Optically Variable Adhesive (OVA), does not have color shift from both sides of the security thread, does not have covert charms, and has no-demet areas in the holographic regions and does not have magnetic elements confined within the color shift pigment.
U.S. Pat. No. 7,054,042 to Holmes et al., hereinafter referred to as '042, disclosed a device employing a demet hologram with a thin film color shifter underneath. The use of a thin film interference filter has a large drawback in terms of color control because the methods employed, vacuum deposition methods, particularly, those that are of such running speeds to make them commercially viable has at best a plus/minus 2% error on the dielectric layer thickness. For a Fabry Perot structure as discussed in '042, a typical design would be Al opaque/Low index i.e. MgF2/absorber Cr 3 nm. With a 2% variation for a 4 QW optical thickness at 550 nm, this thickness variation translates into a delta E color of 27 units and at 6 QW optical thickness at 550 nm translates into a delta E color of 31. From a practical point of view, this color variation makes the distinction between the genuine product and a counterfeit problematical. The only hope to improve the color of a foil with a vacuum process is to have extensive editing which only leads to high a high expensive product.
U.S. Pat. No. 5,700,550 to Uyama teaches the use of an all dielectric optical stack on a holographic forming layer, which has even less control of color than '042, since the structure disclosed by Uyama has five layers of alternating ZnS and MgF2 or TiO2 and SiO2. Each layer is subject to a 2% variation which would result in even larger color variation. Uyama also requires that the device be placed on a black background otherwise if placed on a white substrate the transmissive nature of his device will result in light beams combining from light reflecting from the substrate back through the device with the reflected light beam from the interference stack to produce white light again. Even if the substrate (i.e. currency paper were colored) the light recombination would give low chroma.
The aim of this invention is to eliminate the drawbacks of the prior art so that a new security device having the desired characteristics of a thread for banknotes or other paper documents or even a plastic document have a layered system of counterfeit deterrence that can be manufactured with high quality of color control, along with visible and covert features as well protection for durability on both sides of the device while maintaining a minimum thickness. Therefore, the problem that is being addressed is to provide a new security thread with enhanced features that can easily be assembled. The problem is solved by giving the viewer security features that can be remembered, that has a distinct color shift and covert features for machine or forensic analysis.
It is an object of the invention to provide a simplified multi-layered security device using an optically variable adhesive (OVA).
It is an object of the invention, to provide a thin asymmetric security thread displaying different optical effects when viewed from different sides.
It is another object of the invention, to provide a thin security device with high chroma and high color control.
It is another object of the invention, to provide a thin security thread comprising a demet hologram and covert taggents therein.
It is another object of this invention, to provide a hot stamp image with multilayer security features.